Recurvoides infernus Tyszka, Bubík, and Jach, 2010

Tyszka, Jarosław, Jach, Renata & Bubík, Miroslav, 2010, A new vent-related foraminifer from the lower Toarcian black claystone of the Tatra Mountains, Poland, Acta Palaeontologica Polonica 55 (2), pp. 333-342 : 335-337

Recurvoides infernus Tyszka, Bubík, and Jach sp. nov.

Figs. 3 , 4 , 5 ; Table 1.

Etymology: From Latin inferno, hell, pointing to a hydrothermal vent related habitat of this new species.

Type material: Holotype: UJ 213 P1, Figs. 3 , 5F ; paratypes: UJ 213 P2, Figs. 4A , 5J ; UJ 213 P3, Figs. 4B , 5B ; and UJ 213 P4, Figs. 4C , 5U .

Type locality: Huciański Klin (adit no. 4, see Jach 2002), Chochołowska Valley, Western Tatra Mountains, Poland .

Type horizon: Lower Toarcian , uppermost part of the Banie Ore Bed ,

doi:10.4202/app.2009.0082

a thin horizon of black claystone overlying manganese carbonate/silicate deposits.

Diagnosis.—Test recurvoidiform–pseudoplanispiral; surface coiling composed of 8 to 12 chambers shows one to three abrupt changes of coiling direction; oval aperture rimmed by lip, situated in lower to middle part of apertural face; wall relatively thin, composed of fine quartz grains.

Material.—Over 350 specimens.

Description.—Test is medium in size, and oval and more or less irregularly discoidal in shape. Oval to crescentic, widerthan−long chambers are numerous, 8 to 14 visible on the surface of the test (average 10.5). The chambers are arranged in semi−evolute irregular recurvoidiform coiling with usually one to three abrupt changes of the coiling direction. The usual angle of change is around 45 ° but it may also be about 90 °. “Straight segments” of coiling are composed of 3 to 12 chambers. Longer regular series of chambers in the distal part of coiling cause pseudoplanispiral appearance of the test with 6 to 9 chambers observed around the periphery. The periphery is originally rounded, but angular in compressed specimens. Intercameral sutures are somewhat depressed to indistinct. Relatively thin agglutinated wall, a few grains thick, is composed of medium to fine quartz grains. Aperture is an oval opening rimmed by a lip, areal in position and situated in the lower to middle part of the apertural face.

Dimensions.—Maximum diameter: 0.18–0.445 mm (average 0.313 mm); maximum diameter of the holotype: 0.317 mm.

Variability.—Specimens assigned to the new species display wide variability of the coiling, which is generally a feature of the subfamily Recurvoidinae . When comparing the rollograms of specimens ( Fig. 5 ), the later part of the coiling visible on the surface of the test can be very roughly characterized by two straight series of chambers separated by a change in coiling direction. The final “straight series” of chambers, when it is long enough, gives a pseudoplanispiral appearance to the test. The relatively high variability of the test size can be explained by the presence of juvenile specimens ( Fig. 4B, D ) and gerontic specimens ( Fig. 4A, E ) within the taphocenose.

Remarks.—Thin, organic−cemented walls predisposed squashing of most specimens by compaction during early diagenesis. This squashing resulted in the angulated periphery of compressed specimens. Recurvoides infernus seems to be closely related to Recurvoides baksanicus Makareva, 1969 described from the Aalenian strata of Northern Caucasus in the Kabardino−Balkarian Republic of Russia ( Makareva 1969). The new species differs from R. baksanicus by having more chambers around the periphery (most frequently 7 or 8 comparing with 5 to 7) and larger size (0.18–0.445 mm compared with 0.12–0.30). Other differences cannot be confirmed without direct comparison of the fossil material. R. infernus distinctly differs from R. taimyrensis Nikitenko, 2003 known from the upper Pliensbachian to lower Toarcian of the Barents Sea, Franz Josef Land, and Siberia ( Nikitenko and Mickey 2004) in having a more discoidal shape, pseudoplanispiral appearance, thinner wall, and finer agglutinated grains. Recurvoides taimyrensis is more robust and globular (see Nikitenko and Mickey 2004: fig. 8a–e).

There is no objective method to sort biological species from the fossil foraminifer assemblage ( Benton and Pearson 2001). Our taxonomic decision to isolate this single species is therefore somewhat arbitrary. The observed variability of this Recurvoides assemblage might allow splitting this species into three, four or five taxa. On the other hand, we should be aware that foraminiferal assemblages from stress conditions, such as suboxia, low pH, and hydrogen sulphate or metal pollution may cause development of a high proportion of abnormal tests ( Alve 1991; Yanko et al. 1998, 1999; Geslin et al. 2000; Le Cadre et al. 2003; Polovodova and Schönfeld 2008). This was probably the case with our microfauna, under heavy Mn and Fe pollution and suboxic conditions (see Paleoecology section below). On the other hand, abrupt changes in the direction of coiling are not stable in this genus. The presented rollograms show at least one or two, rarely three, changes of coiling direction roughly of 90 ° or 45 °. Some specimens possess a final evolute pseudoplanispiral portion composed of 7 to 12 chambers that represents the ultimate ontogenetic part of the test. We therefore conclude that most specimens in the studied samples belong to the same species. The thin wall, the texture and composition of agglutinated grains, and overall taphonomic features also support this conclusion.

Geographic and stratigraphic range.—Lower Toarcian, Krížna Unit of the Western Tatra Mountains, the Carpathians, Poland.

Figures

Fig. 3. Ammosphaeroidinid foraminifer Recurvoides infernus sp. nov., holotype, UJ 213 P1, Huciański Klin, Tatra Mountains, sample 3236 (4.8b/1m), Toarcian, wet specimen in reflected light. Original microphotographs with highlighted chambers (A, B) and outline drawings (C), in pseudospiral (A1–C1), peripheral (A2–C2), and side (A3–C3) views.

Fig. 4. Variability of ammosphaeroidinid foraminifer Recurvoides infernus sp. nov., Huciański Klin, Tatra Mts., Toarcian. A. Paratype, UJ 213 P2 (see Fig. 5J for rollogram), sample 3236 (4.8b/1m), in pseudospiral (A1), peripheral (A2), and side (A3) views. B. Paratype, UJ 213 P3 (see Fig. 5B for rollogram), sample 3213 (4.8b/16m), in pseudospiral (B1), peripheral (B2), and side (B3) views. C. Paratype, UJ 213 P4 (see Fig. 5U for rollogram), sample 3237 (4.8a/7.5m), in pseudospiral (C1), peripheral (C2), and side (C3) views. D. Test infilled with pyrite, sample 3236 (4.8b/1m), in pseudospiral (D1–D4), peripheral (D5), and apertural (D6) views; D1, dry specimen in reflected light; D2, wet in reflected light; D3, wet in transmitted light; D4–D6 SEM photographs. E. Strongly compressed specimen, sample 3236 (4.8b/1m), in side (E1, E3) and peripheral (E2) views; E1, specimen in reflected light; E2, E3 SEM photographs.

Fig. 5. Variability of ammosphaeroidinid foraminifer Recurvoides infernus sp. nov., Huciański Klin, Tatra Mts., Toarcian. A–E, W. Sample 3213 (4.8b/16m). B. Paratype, UJ 213 P3. F–Q. Sample 3236 (4.8b/1m). F. Holotype, UJ 213 P1 (see Fig. 3). J. Paratype, UJ 213 P2. R–V, X–Z. Sample 3237 (4.8a/7.5m). U. Paratype, UJ 213 P4 (see Fig. 4B, A, C, respectively).Explanation for rollograms (coiling diagrams):a, position of aperture; b, chamber visible on the test surface; c, chamber covered by the younger coiling; d, chamber partly visible.